Data from such a repository can't be authenticated

I am getting a below error when I do

sudo apt-get update


Reading package lists... Done
W: The repository 'http://download.opensuse.org/repositories/home:    /Horst3180/xUbuntu_16.04  Release' does not have a Release file.
N: Data from such a repository can't be authenticated and is therefore potentially dangerous to use.
N: See apt-secure(8) manpage for repository creation and user configuration details.

Can anyone tell what might be the issue

EDIT: Output of cat /etc/apt/sources.list

deb http://archive.ubuntu.com/ubuntu xenial main
deb http://security.ubuntu.com/ubuntu/ xenial-security main
deb http://archive.ubuntu.com/ubuntu xenial-updates main

First of all make sure that, this works:

sudo rm -rf /var/lib/apt/lists/*
sudo rm -rf /etc/apt/sources.list.d/*
sudo apt-get update

If it did not work, count that, I did not found any other choice for you besides running

sudo apt-get update --allow-unauthenticated

This is a security risk, but if you are ready for this you can use --allow-unauthenticated flag for some other apt commands.